1. Field of the Invention
This invention relates to immobilized cells and a fermentation method utilizing the same. More particularly it relates to immobilized cells prepared by immobilizing aerobic and anaerobic cells in a single immobilizing carrier as well as to a fermentation method utilizing the same, wherein aerobic and anaerobic metabolic sequences are simultaneously carried out to thereby produce a fermentation product.
It is an object of the present invention to economically produce a fermentation product by preparing a carrier which accommodates both aerobic and anaerobic metabolic functions simultaneously and efficiently utilizes these functions.
2. Description of the Prior Art
Martin et al. have reported a fermentation method wherein cells of two microbial strains are simultaneously immobilized by a single carrier (C.K.A. Martin and D. Perlman, European J. Appl. Microbiol., 3, 91 (1976)). However both of these strains are aerobic and there has been no report relating to a fermentation method wherein a combination of aerobic and anaerobic cells is utilized.
Most of the studies on fermentation through the use of microbial cells and processes for industrial production utilizing microbial cells have been carried out by means of so-called pure cultures wherein a single strain is used. Recently demands have arisen for processes for conducting a series of fermentation operations through the use of two or more strains to thereby widen the range of materials to be fermented as well as fermentation products, and to achieve an economic advantage. These demands have led to a development of a so-called mixed culture wherein two or more strains are cultured in a single apparatus, unlike a conventional pure culture wherein the fermentation is carried out by using the same number of culture apparatuses as there are of strains. Although many attempts therefor have been conducted, most of these attempts have been unsuccessful. One principal reason therefor is that in a single culture apparatus wherein each of the ambient factors, such as pH value, temperature or medium composition, should be fixed uniquely, two strains whose optimum culture conditions are not always similar to each other can coexist only in a highly limited range. Even if appropriate conditions can be determined by supposing the coexistence of these cells, they are frequently undesirable for fermentation of either of the two strains. A second principal reason therefor is that when the optimum ambient conditions of two or more strains are identical by chance, these strains compete with each other for medium constituents and, additionally, for oxygen when both strains are aerobic. As a result, these strains are liable to separate into superior and inferior groups, which makes well-balanced coexistence of all cells difficult. When a combination of an aerobic strain requiring oxygen and an anaerobic strain not requiring oxygen is used in a series of fermentation operations, at least the competition between these strains with respect to oxygen can be avoided. Thus, attention need only be paid to the competition between them with respect to medium constituents, which considerably simplifies the setting of culture conditions. However, it is impossible in conventional liquid culture methods to set culture conditions which can simultaneously meet both the oxygen demand and lack thereof in a single culture apparatus. Accordingly, it is generally necessary to employ two culture apparatuses, one of which is set to aerobic conditions and the other of which is set to anaerobic conditions.